279
FXUS02 KWBC 061839
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
239 PM EDT THU AUG 06 2009
VALID 12Z SUN AUG 09 2009 - 12Z THU AUG 13 2009
RECENT MEDIUM RANGE GUIDANCE OVERALL HAS MAINTAINED A CONSISTENT
THEME WITH SOME MODEST DAY TO DAY ADJUSTMENTS. ENERGY WITHIN AN
UPPER LOW/TROF OVER THE NERN PAC AS OF DAY 3 SUN SHOULD PROGRESS
INTO THE NWRN CONUS/SWRN CANADA DURING THE FCST PERIOD... WITH
SOME LINGERING ENERGY LIKELY TO MAINTAIN A MEAN TROF CLOSE TO THE
PAC NW COAST THRU OR BEYOND THE MIDDLE OF NEXT WEEK. MANY GFS
RUNS OVER THE PAST COUPLE DAYS... INCLUDING THE LATEST 00Z/06Z
VERSIONS... HAVE BEEN ON THE FASTER SIDE OF THE MODEL/ENSEMBLE
SPREAD WHILE ECMWF RUNS HAVE BEEN NOTICEABLY SLOWER. A SOLN IN
THE MIDDLE OF THE SOLN SPREAD APPEARS MOST REASONABLE IN LIGHT OF
GFS/GEFS GUIDANCE TRENDING SLOWER WITH LEADING ENERGY OVER THE
PAST COUPLE DAYS AND ECMWF RUNS TRENDING FASTER. FOR THIS CYCLE
THE 00Z ECMWF IS MUCH CLOSER TO THE BEST MODEL/ENSEMBLE CLUSTERING
THAN THE 00Z/06Z GFS.
AHEAD OF THE ABOVE FEATURE... A FAIRLY STRONG RIDGE CENTERED OVER
THE SOUTHEAST AS OF SUN SHOULD WEAKEN AND RETROGRADE INTO THE SRN
ROCKIES. THIS EVOLUTION WILL ALLOW FOR MODERATE AMPLIFICATION OF
NRN PLAINS ENERGY INTO THE EAST BY NEXT TUE-WED. THE CANADIAN HAS
TENDED TO BE A FAST OUTLIER WITH THE INITIAL NRN PLAINS ENERGY AND
GFS RUNS HAVE BEEN ON THE STRONG AND/OR FAST SIDE OF THE REMAINING
SOLN SPREAD ACROSS THE NRN TIER STATES. BY THE TIME THE CORE OF
THIS ENERGY REACHES THE GRTLKS/OH VLY/NORTHEAST... MOST
MODEL/ENSEMBLE SOLNS ARE WEAKER THAN THE 00Z/06Z GFS BUT SUGGEST
THE OVERALL ERN TROF MAY BE MORE AMPLIFIED. THERE IS A DECENT
SIGNAL FROM 00Z/06Z GFS AND 00Z ECMWF/CANADIAN RUNS THAT SOME
ENERGY WITHIN THE EVOLVING ERN TROF MAY CLOSE OFF AN UPPER LOW
CENTER. HOWEVER ENSEMBLES AND THE 12Z/05 ECMWF ARE LESS
ENTHUSIASTIC AND FAVOR ONLY MODERATE WEIGHTING OF A CLOSED LOW
SCENARIO AT THIS TIME. INCORPORATING AN EXTRA DAY OF ECMWF
RUNS... A FOUR-RUN LAGGED AVERAGE IS FAIRLY CLOSE TO THE OPEN WAVE
SOLN OF THE ECMWF ENSEMBLE MEAN BY DAY 7 THU. MEANWHILE AROUND
MON THE 00Z GFS IS AN AMPLIFIED OUTLIER WITH FLOW ACROSS NEW
ENGLAND/EXTREME ERN CANADA. THE 06Z GFS COMPARES MUCH BETTER TO
CONSENSUS THAT INCLUDES THE ECMWF WITH THIS ASPECT OF THE FCST.
FOR THE UPDATED PRELIM FCST... WITH THE 00Z ECMWF COMPARING BEST
TO THE MODEL/ENSEMBLE SPREAD DAYS 3-5 SUN-TUE... ITS SOLN WAS USED
FOR THAT PART OF THE FCST. DAYS 6-7 WED-THU EMPLOYED A 50/50
BLEND OF THE ECMWF AND ECMWF ENSEMBLE MEAN TO ADDRESS THE
UNCERTAINTIES IN SYNOPTIC DETAILS AS INDICATED BY ENSEMBLES AND
OPERATIONAL MODEL CONTINUITY. THIS MAINTAINED REASONABLE
CONTINUITY FROM THE EARLY ISSUANCE.
12Z UPDATE... THE NEW GFS RUN LEANS FASTER THAN THE CORRESPONDING
GEFS MEAN WITH MOST ASPECTS OF SRN CANADA/NRN CONUS FLOW... BUT
COMPARED TO THE FULL SOLN ENVELOPE IN THE LARGE SCALE IT APPEARS A
LITTLE MORE REASONABLE THAN 00Z/06Z RUNS. THE CANADIAN IS STILL A
PRONOUNCED OUTLIER WITH INITIAL NRN TIER CONUS ENERGY AND IS
DISCOUNTED WHILE THE UKMET TIMING IS SOMEWHAT CLOSER TO THE 00Z
ECMWF WITH THAT PORTION OF THE FCST. UPSTREAM THE UKMET IS ABOUT
AS FAST AS THE GFS WITH FLOW ENTERING SRN CANADA BUT LAGS THE GFS
WITH THE TRAILING TROF OFF THE WEST COAST. AT THIS TIME PREFER TO
MAKE NO SIGNIFICANT CHANGES TO THE DAYS 3-7 FCST UNTIL ANY NEW
CONSENSUS EMERGES.
REGIONAL HIGHLIGHTS...
..WEST
OVER THE PAC NW EXPECT DAYTIME TEMPS TO AVERAGE MODESTLY BELOW
NORMAL WITH PERIODS OF UNSETTLED WEATHER IN ASSOC WITH THE MEAN
TROF ALOFT FCST TO BE JUST OFF THE COAST. THE REMAINDER OF THE
WEST SHOULD SEE VARIABLE TEMPS WITHIN A FEW DEGREES OF NORMAL...
AND POSSIBLY SOME SCT DIURNAL CONVECTION OVER AND NEAR THE FOUR
CORNERS REGION.
..CENTRAL/EAST
THE PRIMARY FEATURE AFFECTING THE CNTRL-ERN STATES WILL BE LOW
PRESSURE AND ASSOC FRONTAL SYSTEM GRADUALLY TRACKING FROM THE
PLAINS TO THE EAST COAST. AREAS OF RAIN/THUNDERSTORMS ARE
POSSIBLE ALONG BOTH THE LEADING WARM FRONT AND TRAILING COLD
FRONT. WITHIN THE WARM SECTOR EXPECT AT LEAST 2-3 DAYS OF HOT
WEATHER... WELL ABOVE DAILY NORMALS FOR EARLY AUGUST BUT NOT THE
POINT OF REACHING RECORDS AT MOST LOCATIONS. BY NEXT WED-THU
EXPECT A COOLING TREND OVER THE EAST WHILE THE PLAINS/UPPER MS
VALLEY SHOULD RETURN TO ABOVE NORMAL READINGS. MEANWHILE AWAY
FROM THE DOMINANT CNTRL-ERN CONUS SYSTEM... ANTICIPATE DIURNAL
CONVECTION OVER THE GULF COAST REGION THRU THE PERIOD.
RAUSCH/CISCO
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